PERNICIOUS EXOTIC PESTS AFFECTING FORESTS AND FOREST PRODUCTS IN EASTERN, CENTRAL AND SOUTHERN AFRICA

By

Jeff Odera
Director, KEFRI
P. O. Box 20412
Nairobi, Kenya

INTRODUCTION

With growing sophistication and affluence in external travel and trade, the danger of entry of alien organisms through commercial, private shipment of plant materials and travellers, has become a more pressing problem to forest managers in all parts of the world. Movement of vegetative material for propagation or seed which may be diseased or infested and clothing, soil, humus, peat, compost and lumber are important carriers of all stages and categories or plant enemies. Through movement of these materials, man has facilitated transcontinental spread of many pernicious pests and diseases.

The consequence of spread of foreign pests has been exacerbated by the expansion of industrial forest plantations of fast growing exotic species, particularly conifers and eucalypts.

THE FOREST CROP IN KENYA

The areas of reserved forest estate in Kenya are dangerously small covering only 1.8 Million hectares, (about 3 per cent of the total land area). It is therefore fortunate that the country recognized as early as 1909 (Hitchins 1909) that the indigenous forests could not meet the demand for forest products on a sustainable basis and the trials with fast growing exotic species were begun.

Subsequent silvicultural research concentrated on increasing the yield of this small area of productive forests by converting the non-productive woodlands to fast growing softwood plantations. By 1927 Kenya launched a programme of high-yielding compensatory plantations. Several species of eucalypts and tannin producing acacias were introduced to provide wood fuel and poles. Eucalypts have become established as the windbreak trees in farm holdings beside being the normal source of domestic and industrial wood fuel. Eucalyptus saligna and E. grandis are well established in the highlands and moist low land areas; E. citrodorea is extensively grown as an ornamental tree around Lake Victoria, where it is climatically well adapted. During the last decade E. camaldulensis and E. treticornis have been successfully introduced in the marginal lowland areas.

Sensational success has been obtained with certain exotic softwood species, especially Cupressus lusitanica, Pinus patula and P. radiata in the highland areas. Growth rates are very high hence necessitating specified pruning and thinning treatments in the saw-log circles. Among the pines, P. radiata though the easiest to raise, and a bigger yielder has been gradually displaced by P. patula since 1962 due to its susceptibility to Dothistroma pini.

Several other species of pines have been introduced in Kenya. Among these, P. caribea, P. kesiya and P. oocarpa have been earmarked for afforestation programmes in the lowland areas. Today about 165,000 ha are under man-made forests, comprising some 73,900 ha cypress, 59,600 ha pines and 15,800 ha eucalypts. The rest consist of various indigenous and exotic hard wood species.

Similar developments have occurred in nearly all countries in the region. Today the exotic forest crops in the region extend from the southern Sudan and Ethiopia on the north to the heart of South Africa (a distance of about 10,000 km) and from eastern Zaire to the Arabuko-Sokoke forests off the Indian Ocean on the east coast of Kenya (a distance of 3,000 Km).

The vase extension of single crops over large areas makes our forestry resources extremely vulnerable being exposed to invasion and establishment of many potential pests and diseases of foreign origin. Adis-Ababa, Nairobi, Dar-es- Salaam, Lusaka and Harare lie along the cross-roads of Africa. The greatly increased speed of travel and the ever increasing number of travellers and traffic of goods from different parts of the world are among some of man's activities that may inadvertently aid dissemination and establishment of foreign plant pests and diseases in the region.

EXOTIC FOREST PESTS OCCURRING IN THE REGION

Table 1 summarizes insect pests of economic importance to forestry in the region. Icerya purchasi was reported to be causing damage to A. mollisima in later 50's but was effectively controlled by the predacious coccinellid Rodilia cardinalis and the Agromyzid fly Cryptochaetum iceryae that were introduced from Australia. According to Le Pelley (1968) Orthezia insignis was accidentally introduced into Kenya and Tanganyika many years ago. In the 50's O. insignis caused serious damage to Jacaranda mimosifolia but was later controlled by a beetle Hyperasis jocosa introduced from Hawaii.

Pineus pini was first discovered in Kenya and Tanzania in 1969 (Odera 1974). This pest occurs on about 39 species of pines. Pinus contorta, P. elliotti, P. halapensis, P. massoniana and P. radiata are its most favoured hosts. P. pini is a formidable exotic pest which in the absence of effective control measures attacks and kills healthy trees.

TABLE 1

PERNICIOUS EXOTIC PESTS AFFECTING FORESTS AND FOREST PRODUCTS IN EASTERN, CENTRAL AND SOUTHERN AFRICA

pini is a formidable exotic pest which in the absence of effective control measures attacks and kills healthy trees. Today combined efforts of indigenous predacious insects, and an introduced predator Tetraphleps raoi, and absence of its preferred host trees, such as P. massoniana and P. radiata, appears to keep its numbers within endemic proportions.

Eulachnus rileyi is the second conifer aphid that has been reported in the region (Loyttyniemi 1970, Merchant 1982, Ondendaal 1989 and Odera 1990).

The third and indeed the most devastating conifer aphid to occur in the region, the cypress aphid, Cinara cupressi has been reported throughout Eastern, Central and Southern Africa.

Other foreign pests include Pissodes nemorensis, Ernobius mollis and Cinara cronartii, and seem to be restricted to South Africa. Cryptotermes dudleyi and Stromatium are drywood boring insects introduced from the Indian continent, and are now established in the maritimes of eastern Africa, attack and rapidly destroy structural wood in use.

RECOMMENDATIONS

REGIONAL COLLABORATION

For many years our forests have remained effectively sealed off from Europe and Asia, to the North by the Sahara desert and a secondary barrier of arid land in northern Kenya, to the East by the Indian Ocean, and southward from southern Africa by an expansive scrubland and to the west by the tropical rain forests. Within this zone there is no obvious impediment to pest and disease dispersal. Difficulties in preventing pest and disease spread to us through a continuous land mass, clearly show that the introduction of a destructive alien organism into any new country constitutes as great a threat to any other country in the region.

Admittedly, we cannot keep out foreign diseases or pests for ever, but delay of any duration in entry of any pernicious organism means that money for its control is saved. Moreover, during the intervening period scientists have time to develop control methods including developments of resistant varieties.

INTERNAL CO-OPERATION

It is imperative that each country and indeed the entire region should be able to rely on the validity of phytosanitary guarantees and pedigree work of the exporting country and region and vice versa. Recent experiences in the region has tended to cast doubt on the actual value of foreign certification as a means for preventing or lessening the introduction of harmful alien organisms. It appears that the procedures are not free from risks and however, competently and faithfully carried out, they cannot assure complete

protection. Browne (1948) reported an instance in 1947 when Malayan timber with a good deal of red frass arrived at an Australian port and was inspected by an entomologist who cleared them as harmless. The first observation of infestation of the pine woolly aphid on imported scions at the plant quarantive station at Muguga in 1968 was dismissed as spider webs.

The importance of developing common and indeed uniform plant phytosanitary systems in all the countries of the region is an urgent and imperative task, that must be addressed now.

The efficiency of inspection and certification at the point-of-origin further relies on the abilities of all countries to maintain adequate plant disease and insect surveys and free exchange of information on the occurrence and status of these organisms. Constant surveillance of crops would further enable an early detection of any new pest and disease that may have been introduced. This would enable governments to discover alien organisms while still localized or in an incipient stage and hence amenable to eradication.

A second inspection at the point-of-entry conducted by a competent official provides considerable additional support. It is important for plant inspectors to have adequate knowledge regarding foreign diseases and pests. However, phytosanitary inspection at both ends must involve the services of specialists in plant enemies, particularly in diagnosis of pests and diseases and scientific advice. Scientists and inspectors should maintain an unimpeded flow of information particularly between first-hand information on pests and diseases, methods of inspection and changes in the phytosanitary regulations. Indeed, scientists working on forest protection should be urged to provide information on prevailing forest pests and diseases in their countries and region regularly.

EXTRA RESTRICTION ON IMPORTATION OF VEGETATIVE MATERIAL

Where permanent and complete exclusions is the aim, quarantine procedures must attain an exactitude which cannot be approximated by routine certification methods. It is stressed that quarantine regulations should encourage importation of seed instead of vegetative materials. Vegetative materials including woody cuttings and scions representing some years of growth are bound to be infested by numerous plant enemies that may be difficult to detect or to eliminate by conventional treatment. Some countries through fear of introducing foreign pathogens and pests have developed a very conservative policy on the importation of vegetative materials. However, total embargo on the importation of vegetative materials is bound to harm gainful tree improvement programmes. Understandably, breeders and geneticists are constantly striving to improve the gene pool through breeding

and tree improvement programmes. Importation of cuttings and scion materials must therefore be replaced by materials less prone to carry plant enemies.

Phytosanitary risks may be considerably reduced or even eliminated by limiting imported propagating materials to bud wood to be introduced through a quarantine station. Bud woods are usually clean of plant enemies and indeed, this can be effectively assured through disinfection treatment and conveyance in sterile media. Imported bud wood can be easily mass propagated by meristem tissue culture techniques under post-entry quarantine conditions in the importing country.

SCREENING OF MATERIALS CARRIED BY TRAVELLERS

It is often noted that infringements of Plant Import Regulations largely occur as a result of ignorance. This involves nationals, visitors and members of diplomatic and aid missions. In order to protect our agricultural and forestry crops from the threat of foreign pest invasion, the custom officials must liaise closely with our plant inspectors, and competent plant inspectors should be posted at all entry ports.

WIDER EDUCATION OF THE TRAVELLING PUBLIC

It may be impractical to require that travellers' luggage be treated in the same manner as commercial shipments, so cooperation and understanding by the individual traveller is necessary to prevent the spread of pests. To enable effective cooperation the plant quarantine service should launch public education campaigns at all levels on the functions of plant inspectorate and quarantine services, dangers and risks associated with unrestricted importation of live plant materials. Educational literature should be prepared and passed to heads of department of the universities, national research stations, national missions abroad and resident diplomatic and aid missions.

The customs and quarantine officials can greatly facilitate co-operation of the travelling public by incorporating an appeal to the travelling public n landing cards, as follows:

"You can prevent entry of foreign pests and diseases into Kenya and possible damage and destruction of Kenya's animals, crops and forests. Fresh agricultural products such as meat, plants, seeds and soils can only be brought into Kenya on authorization supported by an import permit duly approved by an appointed officer and on inspection by a government inspector to ensure that these products are free from harmful pest and disease organisms. Diseases and pests brought into the country through agricultural items could cost Kenya billions of shillings and increase the cost of agricultural

and forestry goods to the consumer. Please help Kenya to prevent the entry of these pests and diseases into the country by declaring all animal and plant products on the declaration card."

The card should include declaration regarding inter alia, the bringing into Kenya of: Plants, cutting, grape vines, vegetables, fruits, seeds, nuts, bulbs, roots, soil.

REFERENCES

Browne, F.B. 1948. Insects and the export trade. Malay Forester 11:1-6

Hitchings, D.E. 1909. Report on the forests of the British East Africa. H.M. Stationery Office.

Le Pelley, R.H. 1968. Pests of Coffee. Tropical Science Series, pp. 322.

Loyttyniemi, K. 1959. Eulachnus rileyi Williams. (Homoptera: Lachnidae) infesting pines in Zambia. Ann. Ent. Fermira 45: 116.

Merchant, L. 1981. The pine needle aphid, Eulachnus rileyi Williams. (Homoptera:Aphididae). Pests and Diseases of South Africa. Non. 273:4 pp.

Odendaal, M.R. 1990. Eulachnus rileyi, A new pest on pines in Zimbabwe South African Forestry Journal, 115:69-71.

Odera, J.A. 1974. The incidence and host tress of the pine woolly aphid, Pineus pini (L.) in East Africa. Commonwealth Forestry Review. 53:128-136.

Odera, J. A. 1990. Some opportunities for managing aphids of softwood plantations in Malawi. FAO, FD, MLW/86/20.

PHYTOSANITARY SERVICES IN AFRICA A STRATEGY FOR AVOIDING ENTRY OF FOREST PESTS AND DISEASES INTO THE CONTINENT

By

D. M. Okioga
Director
Plant Quarantine Services
P. O. BOX 30148
Nairobi, Kenya

INTRODUCTION

Kenya is endowed with a vast but under-utilized potential for forestry resources. One of the key roles of the Kenya Forestry Research Institute is to tap this potential through tree breeding and research to suit the requirements of various ecological zones that can support forestry production within the country. The diverse research and tree breeding or selection programmes depend on the availability of a wide spectrum of a gene pool and improved germ plasm which has to be acquired partly through he introduction and exchange of plant genetic materials from all over the world. The importation and exchange of such germ plasm from other parts of the world is imbued with a high risk of introducing dangerous exotic pests, diseases, and noxious weeds.

During the course of the present workshop, various papers have been presented on Cypress Aphid, Cinara cupressi, which has recently been introduced and has becomes established in southern and eastern Africa causing serious damage to the cypress. Indeed the case of the Cypress Aphid serves to emphasize the risk potential inherent in the introduction and spread of an exotic forest pests.

In its original home in Europe, the aphid is a relatively unimportant pest on cypress. However, in southern and eastern Africa, where the pest has recently been introduced, the aphid has caused catastrophic losses to cypress. In an attempt to explain why the aphid has been more destructive in southern and eastern Africa, the following possible facts are offered to account for this occurrence:

1. The introduced pest may have arrived without predators or pathogens which kept it in check in its original home.
2. The pest, which may have been unimportant in its original environment, might have found our environment more to its liking.
3. Cypress plants in our areas may have grown for long periods away from this pest so that genetic divergence evolved resulting plants, which were once relatively resistant, becoming susceptible and hence easily damaged by this pest.

Eradication programmes, to which thousands of dollars was committed by the Government of Kenya, has been without satisfactory results. This is in addition to the millions of dollars being spent annually by both the international organizations and the Kenyan Government in combating this pest. Although the effort by the Government of Kenya and the international organizations on finding a solution to the problem of cypress aphid is commendable, it should be noted that today, the danger still looms and is enhanced by the spread of the pest to new areas.

A lesson to be learned from the introduction of the cypress aphid is that it is essential to keep out all dangerous foreign pests and diseases. The responsibility of taking steps to keep out from our region the dangerous pests and diseases constitutes the main role of the plant quarantine services. In order to achieve this responsibility, the plant quarantine services employs a number of ways. Basically, the service capitalizes on the international Plant Protection Convention, which is administered by FAO. The convention provides for international co-operation in controlling plant pests and diseases and for preventing their international spread. Member parties are charged with providing import permits and phytosanitary certificates in compliance with the International Plant Protection Convention. These documents constitute a written agreement between the government and the person or institution engaged in the business of growing, handling, or moving of plants or plant products or the business of importing or exporting of plants or plant products. The written agreement, made on the documents, legally binds the person to comply with the plant health provisions imposed no the documents.

IMPORT PERMITS

These are documents which are issued to permit the importation of plants and plant materials into Kenya. Import permits cover four categories of plants whose entry into the country is regulated as follows:

PROHIBITED

The plants are totally banned to enter the country except for research purposes and only on the approval by the Director of Agriculture.

QUARANTINE

Significant and destructive diseases may be borne in or on the seed and/or plant materials. Laboratory tests are inadequate and the only safe approach is to reduce the risk by:

1. Limiting the quantity of materials which may be imported.
2. Applying chemical treatment.
3. Growing the imported plant material in isolation. Only after a pathologist has checked the crop with the resultant plant material be released to the importer.

PERMIT

The plants enter the country and released to consignee on issuing of an import permit, for example, the majority of forest tree seeds are imported on permit because they have few seed-borne diseases. However, on arrival, the seeds are inspected by the Plant Protection officials and may be subject to treatment before release. In the event of them being found infected with a dangerous pest(s), disease or weed seed, the Plant Protection official may order for their destruction.

ENDANGERED AND/OR RARE SPECIES

Imported only on the approval by the Government of the exporting country and in accordance with the Convention on International Trade in Endangered Species (CITES) of wild fauna and flora, restrictions are necessary in order to prevent the extinction of imperiled species.

ISSUE OF IMPORT PERMIT

For plant materials under category 1, 2 and 4 above, an import permit is issued by the Plant Quarantine Station. However, for certain plants under category 4, an import permit is issued by the Plant Quarantine Station in consultation with the Wild Life Conservation and Management Department of the Ministry of Tourism and Wildlife. For materials under category 3, an import permit is issued by either the National Agricultural Laboratories or the Plant Quarantine Station or the Chief Grader.

IMPORTATION OF BIO-CONTROL AGENTS AND OTHER LIVING ORGANISMS

Persons intending to import living beneficial organisms, such as bio-control agents, or plant pests, pathogens, or disease vectors, should apply for a permit at least 30 days before the expected shipment date. The application will be considered by a specialist committee, known as the Kenya Standing Technical Committee on Imports and Exports (KSTCIE), appointed by the Director of Agriculture. The committee will be responsible for formulating regulations, including any requirements for special safeguards, related to the importation of the organism. Factors considered include:

Is the organism known to be a significant plant pest? A minor plant pest? or a predator?

Is the organism known to occur in Kenya? If not, does a substitute organism occur in Kenya which could be used instead of importing the exotic one?

If it is a bio-control agent, has the agent been used elsewhere for the control of the target pest? What degree of success is associated with the organism as a bio-control agent? Is it host-specific?

Is the confinement facility secure and is access limited to minimal personnel?

Are field trials included in the test protocol?

Would it be possible to eradicate an outbreak of the organism in case of accidental escape?

Once these factors are considered in detail and importation approved, then the plant quarantine services will issue an Import Permit with additional conditions, where necessary, that are to be observed by the importer.

LAWS OF KENYA VIS A VIS PHYTOSANITARY REGULATIONS

Phytosanitary requirements of various countries include special restrictions or conditions such as:

1. Inspection for pests and diseases specifically mentioned in a country's import regulations.
2. Growing season inspection of parent plants for plant diseases.
3. Prescribed treatments for named pests and diseases which are known to occur in the country of origin.
4. Prohibitions when material originates from specific areas.
5. Freedom from soil.

Phytosanitary Regulations governing the imports of plant materials into Kenya are published in the Plant Protection Act Cap. 234 of the Laws of Kenya. This act sets out the procedures for importation of any form of plant material, seed, fresh fruits, flowers, plantlets, etc. The main features of the Act may be summarized as follows:

All intending importers wishing to bring into Kenya plant materials must obtain a plant import permit from Kenya prior to shipment of such plants from origin regardless of whether they are duty free, gifts, or for commercial or experimental purposes. The permit specifies the requirements for plant health indicating prohibitions, restricted quarantine importations and additional declaration with regard to pre-shipment treatments. The original permit must, therefore, reach the plant health authorities in the country of origin for strict adherence to our permit requirements

Any plant consignment arriving in Kenya, should therefore be accompanied by a copy of our permit and additional health certificate, (phytosanitary certificate, international model or its equivalent) in full adherence to the specifications set out in our permit

Plant materials arriving in Kenya without authority and correct accompanying documents would not be allowed entry and may be destroyed or reshipped at owner's cost

It is illegal to import plants into Kenya without a proper authority from the Ministry of Agriculture.

THE LIMITATIONS OF THE PHYTOSANITARY REGULATIONS

No export or import regulation will entirely prevent the transport of pests and diseases from one country to another. These regulations merely delay the introduction of such noxious pests and diseases. Fungus spores or insects may be carried in air currents. Health certificates, however worded, can never provide absolute guarantee. Therefore, judicious restrictions should only be applied to pests and diseases of quarantine significance to a particular country. It should be borne in mind that if import regulations are too severe and punitive, then there is a real risk that:

Smuggling of plants into the country could be encouraged

Importers may be forced to look for their planting materials, not from countries with the best reporting services and determination to abide by the regulations laid down and agreed, but from countries which have only rudimentary reporting and inspection services, or which are prepared to interpret the requirements loosely

Importation of germ plasm with superior agronomic traits may be impossible and therefore retarding agricultural diversification of the country

The approach adopted for plant imports and exports illustrates the many problems and limitations encountered in plant quarantine service. Quarantine authorities are sometime criticized by importers concerned about restrictions placed on their favourite plants, seed, etc. However such criticism is often short-sighted since plant quarantine service has a wider or longer view and any quarantine restriction or actions have a sound biological basis which ensures both access to overseas development and, at the same time, safety to the country's agriculture and forest resources. The enforcement of quarantine restrictions in Kenya should be viewed positively. We at the quarantine services wish to assure all importers that your quarantine service are tailored to cause as little disruption to the rights of individuals as possible while at the same time we are ensuring that imported plants or plant products do not inadvertently introduce a new pest or disease into Kenya.

SETTING UP OF EASTERN AFRICA SUB-REGIONAL PLANT QUARANTINE SERVICES

Pathogens and pests do not recognize political boundaries. Subsequently, an introduction of a pest or disease in one country will eventually spread across the border to the neighbouring country. A good example is the introduction of the cypress Aphid in Malawi in 1985 and the dramatic spread of the pest to the neighbouring countries including Zimbabwe, Tanzania, Uganda, Kenya, Burundi, Rwanda and Zaire. Similarly, the introduction of the larger grain borer, Prostephanus truncatus Horn, in Tanzania in 1982 has witnessed the spread of the pest to Kenya. Ethiopia is currently wary of the larger grain borer since they are certain that the pest will eventually invade the country. Another pest, the Cassava Mealybug, Phenacoccus manihoti Matile-Ferrero, was reported in the mainland Tanzania in 1987. Since then, the pest has spread to Zanzibar Island and into Kenya. These examples clearly show that it is futile for one country in the region to protect its forests or agricultural crops from foreign pests and diseases through quarantine systems unless her neighbours take similar actions.

Since the eastern African countries (Kenya, Uganda, Tanzania and Ethiopia) share the same geographical location, in the context of African continent, and are still free from some disastrous agricultural as well as forest pests and diseases, it is recommended that the four countries should set up an eastern African Sub-Regional Plant Quarantine Service whose common purpose would be to keep foreign pest diseases out of the region. For example, while pine blister rust, Cronartium ribicola, and nun moth, Lymantria monacha, are serious diseases and pests respectively of coniferous trees. Because these are not known to occur in the region, every precaution must be taken to keep them out.

FAO has supported the set up of the Sub-Regional plant quarantine services in Zimbabwe, for SADCC countries, and in Mali, for Sahelian countries. From reliable sources, FAO would also be willing to give similar financial and technical assistance to enable the setting up of a Sub-Regional Plant Quarantine Service for the eastern African countries. It is anticipated that the Governments of Kenya, Tanzania, Uganda and Ethiopia would equally support the FAO proposal. At the appropriate stage, a Sub-Regional plant quarantine service for the central Africa could also be considered. In this way, the phytosanitary services in Africa, under the umbrella of the Inter-African Phytosanitary Council of the OAU, will be strengthened.

SURVEY AND MONITORING

By

William M. Ciesla
Forest Protection Officer
FAO, Rome

INTRODUCTION

Knowledge of the location of a pest, its population levels and resultant damage is important in pest management decision making. Therefore a comprehensive program of survey and monitoring is essential to support an integrated pest management program.

OBJECTIVES

Survey and monitoring activities may have many objectives. These include:

1. Detection of infestations.
2. Detection of damage.
3. Assessment of seasonal population trends determined by weather conditions, natural enemies, host responses and other factors.
4. Quantification of the effects of infestations for assessment of ecological, social and economic impacts.
5. Assessment of the effects of various treatment tactics.

AERIAL SURVEYS

Damage caused by cypress aphid is highly visible and is distinct enough to not be confused with other types of forest damage. Therefore it lends itself to aerial detection using small overhead wing aircraft such as the Cessna 182, 185 or 210. Aerial "sketchmap" surveys are a key component of forest pest management programmes in North America. They can be done for a fraction of a cent per ha and provide immediate maps of the location of damaged areas. Topographic map coverage at a scale of 1:50,000 already exists for portions of Kenya and recent aerial photo coverage is also available. LANDSAT photo maps are also available which could be adapted for use in aerial surveys. Therefore, an effective aerial detection capability can be instituted within a short time frame to provide updated information on the status of damage.

GROUND SURVEYS

Only the damage caused by the cypress aphid can be detected through aerial surveys. Ground surveys designed to detect and evaluate insect populations must be integrated with aerial surveys. Several types of ground surveys are needed:

1. Surveys to establish presence or absence of the aphid in areas beyond where damage has been detected.
2. Assessment of population density in areas where the aphid has been detected before and after treatment has been applied.
3. Assessment of tree damage to predict the magnitude of growth loss and tree mortality.

Several methods have been used to monitor populations of other tree infesting aphids. The presence or absence of aphid populations can be determined through deployment of traps consisting of microscope slides coated with a thin layer of tanglefoot. This was used with a high degree of success for detection of the balsam woolly adelgid, Adelges piceae, in the southern Appalachian mountains of the United States. In addition, cypress aphid populations can be detected by removing branch samples from mid or lower crowns of host trees with sectional pole pruners and examining them for the presence or absence of aphids. Biological data such as colony size, occurrence of life stages and incidence of natural enemies can be acquired by this method. Sampling intensities required to insure detection can be determined through statistical procedures.

A four class damage rating system has been developed by KEFRI for describing damage on individual trees. This system reflects the progressive dieback associated with cypress aphid infestations from inner crown outward and from lower crown upward. This system has potential application for monitoring rates of damage and possible recovery over time.

REMOTE SENSING

Photos, video or satellite imagery can also provide valuable information. For example, repeated images of sample plantations or natural stands can provide information on rates of decline, mortality or possible recovery. In addition, images taken at intervals following treatment of infestations with chemicals, biological agents or cultural methods can provide valuable information on the effectiveness of these treatments.

SELECTED REFERENCES

Billings, R.F. and C. Doggett, 1980. An aerial observer's guide to recognizing and reporting southern pine beetle spots. USDA Agri. Handbook 560, 19 pp.

Ciesla, W.M., 1984. Mission: Track the gypsy from 65000 feet. American Forests 90:30-33, 54-56.

Ciesla, W.M. and W.E. Bousfield, 1974. Forecasting potential defoliation by larch casebearer in the Northern Rocky Mountains. J. Econ Entomology 67:47-51

Daterman, G.E., R.L. Livingston, J.M. Wenz and L.L. Sower, 1979. How to use pheremone traps to determine outbreak potentials. USDA Forest Service, Agri. Handbook 546, 11 pp.

Dimond, J.B., and R.H. Bishop, 1968. Susceptibility and vulnerability of forests to the pine leaf aphid, Pineus pinifoliae (Fitch) (Adelgidae) Maine Agr. Expt. Sta. Bulletin 658, Orono, Maine, 16 pp.

Heller, R.C. and D.C. Schmeige, 1962. Aerial survey techniques for spruce budworm in the Lake States. J. Forestry 60:525-532.

Lambert, H.L. and W.M. Ciesla, 1967. Status of the balsam woolly aphid in the southern Appalachians. USDA Forest Service, Southeastern Area, Div. Forest Insect and Disease Control, Asheville, NC Rpt 67-1, 15 pp.

Lambert, H.L. and W.M. Ciesla 1967. Impact of summer cutting on the dispersal of the balsam woolly aphid. J. Econ. Entomology 60:613-614.

Livingston, R.L. and G. Daterman, 1977. Surveying for Douglas-fir tussock moth with pheromone. ESA Bulletin 23:172-174.

Mason, R.R., 1979. How to sample Douglas-fir tussock moth larvae. USDA Forest Service, Agr. Handbook 547, 15 pp.

Mason, R.R., 1977. Sampling low density populations of the Douglas-fir tussock moth by frequency of occurrence in the lower tree crown. USDA Forest Service, PNW Forest and Range Experiment Station, Research Paper PNW-216.

Morris, R.F. 1955. The development of sampling techniques for forest insect defoliators with particular reference to the spruce budworm. Canad. J. Zoology 33:225-294.

Odera, J.A. 1991. Some opportunities for managing aphids of softwood plantations in Malawi. Ministry of Forestry and Natural Resources, Malawi and Food and Agriculture Organization of the United Nations, Assistance to forestry Sector - Malawi MLW/86/020 135 pp.

Page C., 1975. The impact of balsam woolly aphid damage on balsam fir stands in Newfoundland. Canad. J. Forest Research 5:195-209.

Waters, W.E., 1955. Sequential sampling in forest insect surveys. Forest Science 1:68-79.

Wickman, B.E. 1979. How to estimate defoliation and predict tree damage. USDA Forest Service. Agr. Handbook 550.

MECHANICAL METHODS AND CHEMICAL CONTROL

By

Julie Weatherby

USDA Forest Service
1750 Front Street
Boise, Idaho, USA 837002

Approximately 175 species of Cinara aphids are known to occur in North American with perhaps more species yet to be described (Voegtlin et al 1986). These aphids have been found on conifers belonging to the families Pinaceae and Cupressaceae.

In North America, Cinara aphids are seldom considered economically important pests within native and planted forests. The literature contains surprisingly few references to growth reduction and branch dieback caused by heavy infestation of Cinara sp. Therefore, research efforts designed to develop pest management strategies for suppressing Cinara sp. have been limited.

More than 25 chemical insecticides are frequently recommended for suppression of aphids infesting agricultural crops. Few insecticides are recommended for control of Cinara sp. Table 1 lists seven such insecticides. These insecticides range from highly toxic compounds such as endosulfan, a chlorinated hydrocarbon, to moderately toxic compounds such as malathion and acephate, two organophosphates.

Most of these insecticides are broad spectrum insecticides. Very little selectivity has been demonstrated towards the pest rather than the natural enemy complex. Zeleny et all (1978), working on insecticides for control of pea aphid, Acyrthosiphon pisum, found that "The selective effect of pesticides is not satisfactory. Contact pyrethroids are less toxic to vertebrates than to arthropods but at the same time they usually affect predators more than prey."

Pirimicarb has been documented as an effective aphicide which is relatively selective favouring the survival of many beneficial insects (Lecrone and Smilowitz 1980, Warner and Croft 1982). The selectivity of pirimicarb, a carbamate insecticide, has been demonstrated frequently in areas where consistent use of organophosphate insecticides has lead to resistance in aphid populations. Pirimicarb is no longer registered in the USA mostly because the size of the market was deemed too small to be profitable.

TABLE 1
CHEMICAL INSECTICIDES RECOMMENDED FOR USE ON CINARA SP. IN THE PACIFIC NORTHWEST, USA, 1990

Sources of Information:

Pacific Northwest Insect Control Handbook, 1990. Cooperative Extension Services, University of Idaho, Oregon State University and Washington State University.

Farm Chemicals Handbook, 1990. Meister Publishing Co., Willoughby, Ohio.

^a Class I: Oral LD 50 < 50 mg/kg, Dermal LD 50 < 200 mg/kg.

Class II: Oral LD 50 - 50 to 500 mg/kg, Dermal LD 50 - 200 to 2,000 mg/kg.

Class III: Oral LD 50 - 500 to 5,000 mg/kg, Dermal LD 50 - 2,000 to 20,000 mg/kg.

Class IV: Oral LD 50 > 5,000 mg/kg, Dermal LD 50 > 20,000 mg/kg.

^b Not registered in the USA.

Application equipment which has been or might be used in chemical suppression projects range from small, hand- pressurized equipment to aerial application equipment. Equipment selection is partially dependent upon the size of the host trees to be sprayed, the structure of the canopy, and the location of aphid feeding sites. With low-volume aerial applications, penetration through the foliage to the branches is difficult. With high volume, high pressure, hydraulic applications, complete wetting of the branch surface is possible, but the operation is costly in terms of time and chemical. Airblast sprayers commonly used in orchard management are capable of spraying 15- to 18-meter-tall conifers if the row and inter-tree spacing is such that the canopy is not closed. Airblast sprayers can be effective if the application speed averages between l.,5 and 2.5 kilometres per hour under relatively calm wind conditions.

In summary, there are many questions which must be discussed before use of chemicals can be recommended as aphid pest management tools in conifer plantations of Africa. Hopefully, we, the participants in this Workshop, will be able to address many of the issues and questions which will surface as we discuss the role insecticides might play.

REFERENCES

Lecrone, S and Z. Smilowitz. 1980. Selective toxicity of pirimicarb, carbaryl and methamidophos to green peach aphid (Myzus persicae) (Sulzer), Coleomeailla maculata lengi (Timberlake) and Chrysopa oculata Say. Environ. Entomol. 9(6): 752-755.

Voegtlin, D., G. Remaudiere, and R. Pena Martinez. 1986. New and little known aphids from Mexico. Proc. Entomol. Soc. Wash. 88(2): 227-236.

Warner, L.A. and B.A. Croft. 1982. Toxicities of azinphosmethyl and selected orchard pesticides to an aphid predator, Aphidoletes aphidimyza. J. Econ. Entomol. 75: 410-415.

Zeleny, J., J. Vostrel, Z. Ruzicka, and P.K. Kalushkov. 1987. Impact of various pesticides on aphidophagous coccinelids. In Ecology and effectiveness of Aphidophaga: Proceedings of an International Smposium, Teresin, Poland, August 31 - September 5, 1987. Eds. E. Niemczk and A.F.G. Dixon. SPB Academic Pub., The Hague, Netherlands. 341 pp.

SILVICULTURAL METHODS OF EXOTIC APHID  PEST CONTROL: USE OF RESISTANT STRAINS OF HOST TREES

By

F. Owino
International Council for Research in Agroforestry
Nairobi, Kenya

INTRODUCTION

It is important that foresters accept and be prepared to overcome technical challenges brought about by inevitable pest outbreaks - particularly when working with exotic tree species. Upon confirmation of widespread infestation by a new pest, five questions must be addressed by both the silviculturists and entomologists:

1. Could pesticide control work and still stay within economic limits and environmental safety?
2. Could biological pest control methods be relied on to save the present and future plantations?
3. Could silvicultural manipulation control the pest?
4. Would it pay to breed strains of trees that are resistant to pests?
5. What is the economic impact of the present and projected infestation as assessed from tree mortality, growth reduction, wood quality, etc.

With the growing awareness of the environmental risks associated with chemical pest control, greater attention is now given to biological and/or silvicultural methods of pest control in agriculture and forestry. Silvicultural control of pests could be realised through gradual or sudden switch to alternate tree species, use of multi-clonal and multi-species mixes in raising plantations and pest resistance breeding.

It will often prove necessary to integrate immediate and long term solutions to new infestations. thus, there could be multiple solutions involving salvage cuttings, pesticide application, switch to alternative species or breeding for pest resistance.

TREE GROWTH AND THE POTENTIAL IMPACT OF APHID INFESTATION

In assessing the potential impact of aphid infestation, it is useful to disaggregate the biological yield of the tree into component leaf area controlled physiological processes and wood produced on the stem. It has been established in plant growth analysis that the rate of increase (⌂W) in biological yield is related to the mean leaf area (L) and the net assimilation rate (NAR) as follows:

⌂W = NAR X L

Where: NAR refers to plant dry weight accumulated per unit of leaf area per unit of time.

Thus the area of photosynthesizing surface (leaf) is a dominant determinant of biological yield. Furthermore in conifers, the photosynthate source-to-sink chain is such that biological yield is strongly and positively correlated with economic yield.

Aphid infestation reduces photosynthesizing leaf area and, When severe, results in mortality. Aphids also exude a sugary liquid which often serves as a centre of infestation for fungi. This secondary effect of aphids could be important for species like Cupressus lusitanica which are susceptible to diseases like cypress canker caused by the fungus Monochaetia unicornis.

With respect to the wood produced, it should be recognised that not only will the total wood produced be reduced upon infestation but the quality of wood may be reduced substantially. This would be particularly so if the aphid attack is associated with disease infestation.

SWITCH TO ALTERNATIVE SPECIES

In those cases where chemical, biological and silvicultural control methods all appear unfeasible or beyond economic limits, alternative species should be considered. However, such decisions should not be taken casually as the proposed alternative species will invariably be attacked by its own pests and diseases at later stages.

With species reference to the current attack on cypress trees by the aphid Cinara cupressi, the following aspects are worth highlighting. Cupressus lusitanica and C. torulosa are important plantation species in highland zones of eastern and southern Africa. For example in Kenya, C. lusitanica comprises about 40% of the plantation area. Both species are among the fastest growing exotics and produce high grade sawn timber for construction and joinery work. Another species, C. macrocarpa grows even faster on similar sites but is no longer planted due to high susceptibility to cypress canker. In trade terms, it would be difficult to substitute cypress timber with those of other fast growing candidates like pines and eucalypts. Furthermore, observations in Kenya, Rwanda, Burundi and Zimbabwe have confirmed that Cinara cupressi can attack all members of the Cupressaceae although it is particularly damaging to the C. lusitanica, C. lindleyi, C. benthamii, C. macrocarpa group. All in all, a switch to alternative species does not appear to be a plausible option and therefore, other methods of control must be explored.

DEVELOPMENT OF RESISTANT STRAINS OF HOST TREES

Besides biological control of the pest, research efforts should focus on developing resistant strains of host trees. Field observations indicate that some individuals are relatively free of the pest within badly infested zones. This could be due to one or combinations of the following:

1. Pest Escape - This is unlikely given the rapid spread of the aphids.

2. Physiological resistance - Ability to "repel" pests during periods of rapid growth.

3. Dynamic Defenses by the Host Tree - Such as release of toxic phenols.

4. Tolerance - Capacity of the tree to grow despite infestation.

Both 3 and 4 above could have inheritance basis and could be relied on in breeding programmes. It must be stressed, however, that it rarely pays to launch an extensive pest resistant tree breeding programme. For one thing, genetic gains from such efforts are hard to quantify as they are intricately tied to fluctuating infestation intensities. An even greater problem is that the possibility that the pest may change in population dynamics and host preference over time. Earlier experiences with pine woolly aphid attest to this.

PROPOSAL FOR INTEGRATED SOLUTION

It is proposed that an integrated solution, which combines biological control of pests with selection and breeding for resistant strains of host trees be adopted. One the side of breeding for resistant trees, research should focus on the genetic basis of observed resistance to the aphid and gains that can be derived through selection and breeding.

PROSPECTS FOR THE BIOLOGICAL CONTROL  OF EXOTIC FOREST APHID PESTS  IN SOUTHERN AND EASTERN AFRICA

By

S. T. Murphy, Y. J. Abraham and A. E. Cross
International Institute of Biological Control
Silwood Park
Buckhurst Road
Ascot
Berks SL5 7TA, United Kingdom

INTRODUCTION

The three African aphid pests, Cinara cupressi (Buckton), Eulachnus rileyi Williams (Homoptera: Lachnidae) and Pineus sp. (Homoptera: Adelgidae) have originated from other continents where, as far as recent records are available, they are not considered major pests. This exotic origin of the aphids makes them particularly amenable to "classical biological control". This method of biological control seeks to select important specific regulatory enemies from the area of origin of host and to introduce these species through a strict quarantine procedure into the area where the host is uncontrolled.

In this paper, two criteria are used to assess the potential for the biological control of the three aphid pests: the occurrence of suitable natural enemies in the respective areas of origin of the aphids; and the results of other biological control programmes against lachnid and adelgid forest pests. Much of the information presented in this paper has recently been summarized by Mills (1990).

AREAS OF ORIGIN AND NATURAL ENEMY COMPLEXES

CYPRESS APHID (CINARA CUPRESSI)

This aphid, like other members of the genus, is usually found throughout the warmer parts of the Holarctic region although Eastop (pers. comm.) considers the centre of origin of the species to be Europe. In Europe the aphid feeds on various species of Cupressus, Juniperus and Thuja (Carter and Maslen 1982).

In their native range, Cinara species, like other conifer lachnids are attacked by hymenopterous parasitoids and by insect predators including coccinellids, syrphids, hemerobiids, chrysopids and heteroptera (Mills 1990). The hymenopterous parasitoids are the most host specific of these natural enemies and, as such, tend to have a more significant impact on their host species. All of the important

parasitoids belong to one family, the Braconidae (Haguar and Hofsvang 1991) and within this family, Pauesia species seem to be particularly important (Stary 1966; 1976).

Although few studies have been conducted on the natural complex of C. cupressi several records of possible insect parasitoids and predators do exist in the literature (Table 1). It seems that several parasitoids may attack this species and furthermore, most records to date are from the Palaearctic region which gives further support to the hypothesis that the aphid originates from the old world.

Besides the specific parasitoids listed in Table 1, other parasitoids which are specific to Cinara species that feed on the Cupressaceae, for example, Pauesia cupressobii Stary (Stary 1966), may be important candidates for the control of C. cupressi.

PINE NEEDLE APHID (EULACHNUS RILEYI)

This species is Holarctic on distribution but, like the cypress aphid Eastop (pers. comm) considers the species to have originated in Europe.

The pine needle aphid has similar groups of natural enemies associated with it as the cypress aphid. Particular records for the species are shown in Table 2. Diaeretus leucopterus Haliday is of particular interest as Stary (1966) considers that this parasitoid has the potential to control host outbreaks.

PINE WOOLLY APHID (PINEUS SP.)

The African Pineus sp. shows morphological characteristics that are similar to both P. pini (Macquart) from Europe and P. laevis (Maskell) from North America (Murphy, this workshop). As a number of biological control programmes against both these temperate species have already been executed earlier this century for other regions of the world, for example, New Zealand (Zondag and Nutall 1989) and Hawaii (Culliney et all 1988), the natural enemy complex associated with Pineus sp. are well known, particularly for P. pini (Table 3).

Pineus pini, like other adelgids is attacked by a range of aphidophagous predators including chamaemyiids, syrphids, coccinellids and hemerobiids (Mills 1990), but unlike lachnids it is not attacked by hymenopterous parasitoids. The predatory groups include both relatively host-specific and more generalist species but it is the former group which are of interest for biological control work. Of particular interest are the various species of Leucopis (Diptera: Chamaemyiidae) as some of these species, for example, L. tapiae are specific to Pineus species and have already been successfully used for the control of P. pini and P. laevis in other regions of the world. The biology of l. tapiae, a

TABLE 1 NATURAL ENEMIES OF CINARA CUPRESSI

TABLE 2 PARASITOIDS OF EULACHNUS RILEYI

TABLE 3 PREDATORS OF PINEUS PINI IN THE UK AND EUROPE

Holarctic species, has been studied by Eichhorn (1972) and to a certain extent is typical of the group. All life cycle stages are found associated with the host and in Europe the fly is bivoltine. The eggs are laid singly under the wax covering of the adult prey and pupation occurs at the larval feeding sites. In the laboratory the development time from oviposition to adult emergence is 26.5 days at 21⁰ C.

Other host specific predators of Pineus species include Scymnus species (Coleoptera:Coccinellidae) and Lestodiplosis pini Barnes (Diptera:Cecidomyiidae).

PREVIOUS BIOLOGICAL CONTROL PROGRAMMES AGAINST CONIFER APHIDS

There are many precedents for successful biological control of exotic pests in forestry systems (Dahlston and Mills 1990). Indeed, successful programmes have already been completed against P. pini and P. laevis in a number of regions of the world (Table 4). Thus, a devastating outbreak of P. pini in Hawaii, which occurred in the 1960's, has been successfully controlled by the introduction of two chamaemyiids, Leucopis obscura from Europe and L. nigraluna McAlpine from Pakistan (Nakao et al 1981). Likewise, P. laevis has been successfully controlled in New Zealand by the introduction of Leucopis tapiae (Zondag and Nuttall 1989) and in Chile by the introduction of L. obscura (Zuniga 1985).

Similar successes in biological control have been achieved against a number if lachnid pests (Table 4). The pine lachnid, cinara cronartii (Tissot & Pepper), a North American species that was found infesting pines in South Africa in the late 1970;s, was successfully controlled by the introduction of the specific parasitoid, Paueusia sp. from the southeastern USA (Kfir et al 1985). Furthermore, a classical biological control programme is currently under way in France against the cedar aphid, Cedrobium lapportei Remaudiere, which originates from Morocco. The specific parasitoid Pauesia cedrobii Stary and LeClant has been established in France on the pest but it is yet too early to assess the results of the programme (Fabre and Rabasse 1987).

DISCUSSION

Forest insect pests can be controlled by several methods including silvicultural, pesticidal and biological control techniques. Silvicultural options include replacement of the plantations and social forestry systems with the species that are more resistant to the pests. This is not a feasible short-term solution for the established plantations in southern and eastern Africa.

TABLE 4 
SUMMARY OF BIOLOGICAL CONTROL PROGRAMMES AGAINST ADELGID AND LACHNID CONIFER PESTS (FROM MILLS 1990)

Chemical pesticide applications can sometimes provide a temporary solution to forest pest problems but the cost of such treatments is frequently prohibitive, in terms of both pesticides and application. Furthermore, it is difficult to achieve, by means of conventional spraying equipment, adequate coverage of pesticides in a forest canopy.

By contrast, classical biological control, the use of natural enemies from the area of origin of the host, is a popular and successful means of controlling pests in plantation forestry (Dahlston and Mills 1990); The Homoptera are particularly suitable for control by this method (Greathead 1989). Biological control is not disruptive to the forest environment since its action is very specific to the target pests and once implemented provides lasting control of the pest with no need for any further intervention.

It is clear from the studies on the natural enemy complexes of the aphids in Europe that specific natural enemies, suitable for trial against the aphid in Africa, do exist. In the case of Pineus sp., the various species of Leucopis should be screened for trial especially in view of the successes achieved with these parasitic flies in biological control programmes in other parts of the world. In the case of lachnids, the parasitoid Diaeretus leucopterus should be screened for trail against E. rileyi and Pauesia species for trail against C. cupressi. However, in view of the lack of information about the natural enemy complexes of these lachnids, further efforts need to be made to study these complexes in the respective areas of origin of the aphids.

REFERENCES

Carter, C.I.; Maslen, N.R. 1982). Conifer Lachnids. Forestry Commission Bulletin No. 558, 78 pp.

Culliney, T.W., J.W. Beardsley, J.J. Drea 1988. Population regulation of the Eurasian pine adelgid (Homoptera:Adelgidae) in Hawaii. Journal Economic Entomology 81, 142-147.

Dahlston, D.L., N. J. Mills 1990. Biological control of forest insects. (in press). In Fisher, T.W. (Ed) Principles and application of biological control. California University Press.

Eichhorn, O. 1971. Biologische Bekampfung der nach Ostrafrika eingeschleppten Keifern-Wollaus Pineus sp. (boerner: ?) Beitrage zur Tropenforst Forschung 1972, 31-46.

Fabre, J.P, J.M. Rabasse 1987. Introduction dans de sud - est de la France d'un parasite: Pauesia cedrobii (Hym.:Aphidiidae) du puseron: Cedrobium laportei (Hum.:Lachnidae) du cedre de l'atlas: Cedrus atlantica. Entomophaga 32:127-141.

Greathead, D. J. 1989) Biological control as an introduction phenomenon: a preliminary examination of programmes against Homoptera. Entomologist 108:28-77.

Gunkel, W. 1963. Cupressobium juniperinum Mordv. (Homoptera- Lachnidae), ein Schaedling an Thuja occidentalish. Beitrag zu seiner Morphologi uniologie. Zeitschrift Fur Angewandte Zoologie 50:1-48.

Hagvar, E.B., and T. Hafscang 1991. Aphid parasitoids (Hymeoptera, Aphidiiae): biology, host selection and use in biological control. Biocontrol News and Information 12:13-41.

Kfir, R., F. Kirsten, H.J. van Rensburg 1985. Pauesia sp. (Hymenoptera: Aphidiidae): a parasite introduced into South Africa for biological control of the black pine aphid, Cinara cronartii (Homoptera:Aphidiidae). Environmental Entomology 14: 597-601.

McLean, I.F.. 1982. Three species of Leucopis Meigen (Diptera: Chamaenyiidae) new to Britain. The Entomologist's Record and Journal of Variation 94:70-72.

Mills, N.J. 1990. Biological control of forest aphid pests in Africa. Bulletin of Entomological Research 80:31-36.

Mustafa, T.W. 1987. Reproductive biology and population studies of cypress aphid Cinara cupressi (Buckton) and pine aphid C. maritimae (Dafourl. Dirasat 14, 99-105.

Nakao, H.K., G.X. Funasaki, S.Y. Higa and P.Y. Lai 1981. Introductions for the biological control in Hawaii 1977 and 1978. Proceedings of the Hawaiian Entomological Society 23, 425-430.

Stay, P. 1966. Aphid parasites of Czechoslovakia. 242pp. The Hague, Dr W. Junk.

Stary, P. 1976. Aphid parasites of the Mediterranean area. 95 pp. The Hague, Dr W. Junk.

Tremblay, E. 1975. The parasites of the aphids of Pinus nigra Am. (Hymenoptera:Ichneumenoidea). Bulletino del Laboratorio di Entomologia Agraria Portici 32:91-110.

Wilson F. 1960. Notes on the insect natural enemies of Chermes with particular reference to Pineus pini. Koch and P. strobi Hartig. Bulletin of Entomological Research 29:337-389.

Zonda R., M.J. Nutall 1989. Pineus laevis Maskell, pine twig chermes or pine woolly aphid (Hemiptera: Adelgidae). In Gameron, P.J., Hill, R.L., Bain, J. & Thomas W.P. (Eds). A review of invertebrate pests and weeds in New Zealand 1874 to 1987. Technical Communication CAB International Institute of Biological Control No. 10:295-297.

Zuniga, E. 1985. Ochenta anos de control biologico en Chile, revision historcia y evaluacion de los proyectos desarrollados (1903-1983). Agricultura Technica (Chile) 45:175-183.

COMPATIBILITY OF TACTICS: AN OVERVIEW

By

Melvyn J. Weiss
Assistant Director, Forest Pest Management
USDA Forest Service, Washington, D.C., USA

Yesterday, and today speakers have discussed several tactics, or tools, that should be considered in an integrated pest management approach to the cypress aphid. Seven categories of tactics were discussed: quarantine, survey, chemical control, silvicultural manipulations, mechanical control, genetic resistance and biological control.

This paper is a brief overview of comments by previous speakers with some comments added by this author. Each tactic is discussed along with its advantages and disadvantages. Compatibility between the tactics is also discussed. This paper is necessarily brief and excludes important details provided by the other speakers.

Quarantine - This tactic includes regional collaboration, quarantine enforcement and education of travellers. The advantage of quarantine is the exclusion of additional pests which could threaten the exotic plantations. The obvious disadvantage is that the immediate problems of the cypress aphid and the other two aphids are not addressed by quarantine.

Surveys and monitoring - This tactic is essential in making sound pest management decisions. The major advantages are providing early warning of pest problems, and providing the information needed to decide when and where to take action. A major problem at this time is the lack of research on methods for surveying, estimating and evaluating aphid populations, and aphid damage.

Chemical control - Several chemicals are available that would probably work against the cypress aphid. If chemicals worked, the advantage would be a fast way to protect trees. Disadvantages are several and include potential adverse effects on parasites and predators; environmental concerns particularly if multiple treatments were carried out; if chemicals alone were used, potential perpetuation of the forest conditions that favour the aphid; lack of research on application including rates of application and methods to ensure that the chemical reaches the aphid; and potential management dependency on chemicals to the detriment of work on the other tactics. Some chemical use may be appropriate but only if care is taken to minimize undesirable effects.

Si1vicultural manipulations - This tactic includes possible use of alternative species, selection of sites unfavourable to the aphids, thinning susceptible plantations to expose light-sensitive aphids and improve tree vigour, planting more than one species in the same plantation and accelerated harvest of damaged stands. The major advantage of a silvicultural approach is long term change in forest conditions so that stands are no longer highly susceptible to aphid infestations. There are some significant disadvantages. The most serious disadvantage is that most of the methods have not been rigorously tested and evaluated. In the case of accelerated harvest, there is a lack of adequate markets.

Mechanical control - This tactic would include the trapping of aphids on sticky traps or similar devices, and high volume applications of water to physically wash aphids off branches. Advantages would include few or no negative environmental effects. There are some disadvantages for use of this tactic. The tactic has not been tested and evaluated for control of cypress aphid. It is also likely to be labor intensive, and, in the case of traps, more applicable for survey than for control.

Genetic Resistance - Several observers have noted variation in susceptibility to cypress aphid within or between species, suggesting the potential for selection or the planting of alternative species. The major advantage of selection within species would be the potential for continued use of C. lusitanica. and the possibility of capitalizing on observed resistance in trees already established. There is uncertainty whether the observations indicate resistance to attack (aphid finds the tree unsuitable) or tolerance to attack (aphid attacks, but tree is undamaged) and whether the resistance or tolerance observed will be sustained over time as there are additional aphid attacks. This suggests the need to make observations over a longer time period before beginning a genetics program. A major problem in shifting to other species is that other candidate species are not of equal quality to C. lusitanica.

Biological Control This tactic includes the introduction of natural enemies of cypress aphid. Two approaches would be used in concert: 1) classical biological control or the use of natural enemies introduced from areas where the cypress aphid is indigenous, and 2) natural enemies, if any, in Africa to complement the classical approach. This tactic has a high potential for success based on previous successes with similar pests elsewhere, and the likely availability of candidate natural enemies in North America and Europe. Disadvantages include the possibility that the tactic may not provide immediate results, and incompatibility with widespread use of chemicals.

Development of an integrated pest management approach will require an in-depth examination of these tactics to determine the most effective combination. The most effective combination will likely vary by region, so the general integrated pest management approach will need to be flexible and adaptable. Also, the approach will need to consider that some tactics may not be compatible.

Development of an integrated pest management approach should be a dynamic, evolutionary process starting with the proven or most promising tactics, and adding additional tactics as research and development on new methods is completed. There will also likely be a continuing need for a balance between short and long-term solutions, since neither short or long-term solutions, alone, are likely to be sufficient. There will also be a need to ensure that as many tools as possible are available so that the program is not overly dependent on a few methods which could, over time, prove ineffective or undesirable.

The goals of an integrated approach should be to provide solutions which are long-lasting, less costly over the long- run, and have a minimum of undesirable effects on the environment.

IMPACT OF THE CYPRESS APHID OUTBREAK  ON THE FOREST INDUSTRY OF KENYA

By

J. O. Gor
Chief, Industrial Forestry Division
Forestry Department
Kenya

INTRODUCTION

Since the initial detection of the cypress aphid in March 1990 at Kiserian, the pests have been confirmed in a number of areas throughout Kenya. The insect is present throughout the Nairobi Province. In the Rift Valley province it is present in the Narok, Nakuru, Kajiado, Uasin Gishu, Nandi, Trans- Nzoia, Baringo, Elgeyo Marakwet, Laikkipia and Kericho Districts. In the Eastern Province, it is present in the Machakos, Embu and Meri districts. In the Central Province, it has been detected in the Kiambu, Muranga, Nyandarua, Kirinyanga and Nyeri Districts. In the Nyanza Province, cypress aphid occurs in the South Nyanza, Kisii, Nyamira, Kisumu and Siaya Districts and in the Western Province, it occurs in the Busia, Bungoma and Kakamega Districts.

In all, the aphid has been reported in 27 districts in the country where host trees are found. The effects of attack by the pest appear more pronounced during the dry periods and on poor sites, on mature trees and scattered individual trees on farms. Apparently, the rate of spread is slower in high altitude (cold) areas. It has been observed, that with the onset of rains, there have been recoveries on some of the trees which had not completely dried up during the initial attack. Also hedges around Nairobi, which had been sprayed continually with suitable chemicals before the effect of the aphid attack had become visible have remained healthy where spraying has been done from time to time.

Reinfestation has been observed in parts, of some districts during the dry spells that have followed the lulls during the heavy rains. This has serious implications on the future of the host trees, particularly cypress, in kenya. At stake are the 86,000 ha of cypress and cedar trees in industrial plantations in the government forest estates. In addition, it is estimated that there are some 30,000 ha equivalent of cypress woodlots, shade trees and hedges on farms and towns throughout the country which are also threatened. These estimates do not include the indigenous cedar trees scattered over an area of about 280,000 ha in the Kenya Highlands. Should all these resources be ultimately destroyed by the pest, Kenya stands to lose about US $ 8 billion worth of timber products, not considering the environmental effects on the catchment areas whose values may be higher though difficult to measure in monetary terms.

SALVAGE AND PROCESSING OF DAMAGED CYPRESS

The biggest concern of the Kenya Government at this stage is how she would handle materials that would become available in the country within a very short time if an effective control measure cannot be developed in the near future. Over 60% of the cypress and cedar trees in the government forest estates are of commercial sizes, these would yield a minimum of 21 m³ million of round logs. The local (Kenya) markets, unfortunately, can only absorb a maximum of about 1.2 m³ of round logs per year composed of various species (cypress being about 0.7 M³ million.

Following the recent heavy deaths of individual trees scattered in farmlands, the government, through forest extension agents, advised farmers to undertake salvage operations and dispose of the materials by converting them locally into sawn timber of selling them to established saw millers and other wood users. This exercise has apparently resulted in an over supply of cheap materials from the farms and this has caused a glut in the marketing of sawn timber in the country. Large and established sawmills with heavy overheads, have found themselves unable to dispose Of their sawn timber at the normal prices. They have had to sell them at almost throwaway prices to compete with suppliers of farm materials. This has tended to affect the sawmill industry in the country adversely. This situation is expected to become even worse for the industry when salvage operations start in government forest estates. An advance arrangement must therefore be made on how to store or dispose of excess cypress and cedar materials over long periods of time (over 30 years at the present consumption rate) may prove too costly for the government. There may be a need to create external markets to enable the material to be disposed of in the shortest time possible. It may even be necessary also to consider contracting harvesting of the materials to foreign firms who have the skills and resources to undertake urgent large-scale logging operations. It may also be necessary to consider extending the rotation age of pine species in the interim period to allow for intensified utilization of cypress in the country and reserve the pines to meet the future needs of the country.

FUTURE PROSPECTS

With the outbreak of the cypress aphid, the earlier projections of self sufficiency in wood products to the year 2030 now looks rather bleak. The Pan African Paper Mills, which has been using cypress as part of its materials (35% of log intake) may need to consider intensifying intake of alternative species. Faster growing species, such as Eucalyptus will need to be planted in increased proportions in the future to be able to rescue the industry from collapse due to shortages of materials.